Synthesis of glyoxalic acid using methyl dichloroacetate by microwave method

Article abstract of DOI:10.14233/ajchem.2014.15616

Microwave irradiation was used to synthesize glyoxalic acid from methyl dichloroacetate. The effects of the irradiation time, reaction temperature, reactant ratio and different alkali on the yield of glyoxalic acid were studied and also compared with thos

Full text of DOI:10.14233/ajchem.2014.15616

Asian Journal of Chemistry; Vol. 26, No. 7 (2014), 1995-1997
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.15616
Synthesis of Glyoxalic Acid Using Methyl Dichloroacetate by Microwave Method
*
QIAN NIU, XIONG LUO, SHOU-GAO LI, YING MENG and FU-XIANG LI
Research Institute of Special Chemicals, Taiyuan University of Technology, Taiyuan 030024, Shanxi Province, P.R. China
*Corresponding author: Fax: +86 351 6111178; Tel: +86 351 6010550-3; E-mail: L63f64x@163.com; rencizhe@126.com
Received: 10 April 2013;
Accepted: 17 June 2013;
Published online: 22 March 2014;
AJC-14945
Microwave irradiation was used to synthesize glyoxalic acid from methyl dichloroacetate. The effects of the irradiation time, reaction
temperature, reactant ratio and different alkali on the yield of glyoxalic acid were studied and also compared with those effects under
conventional heating. The yield of glyoxalic acid can reach 84.6 % within 6 h under the microwave irradiation, which is 12.2 % higher
than that under conventional heating within 12 h. The optimum reaction time is 7.5 h and the optimum reaction temperature is 75 °C under
the microwave irradiation. The results indicated that microwave irradiation was superior to the conventional heating obviously.
Keywords: Microwave irradiation, Methyl dichloroacetate, Synthesis, Glyoxalic acid.
time in organic synthesis. The microwave irradiation method
has been applied to many kinds of reactions in organic synthesis
and is becoming one of the hot point for green chemical reaction
lately.
INTRODUCTION
Glyoxalic acid, the most simple keto acid, has properties
of both acids and aldehyde, which could be found in some
animal's body fluids and unripened fruits. As an important
organic synthesis intermediate, glyoxalic acid can be widely
applied in fine chemicals synthesis, such as varnish, medicine,
dyestuff, spicery, plastics additives and industrial chemicals.
It can also be used in the production of oral penicillin, vanillin
and allantoin, etc1.
The yield of glyoxalic acid from the hydrolysis reaction
of methyl dichloroacetate under conventional heating method8
is only 70 %. We have reported a novel microwave heating
technique as an alternative to the conventional heating in
synthesis of glyoxalic acid. This paper aims to explore the
speed and degree of reaction under the condition of microwave
and to find the optimal reaction conditions for the synthesis of
glyoxalic acid, to provide application foundation and technical
support for comprehensive utilization of methyl dichloro acetate.
The reaction equations are described as follows:
Several techniques have been reported to produce
glyoxalic acid including, oxidation of glyoxal2,3, ozonation of
maleic acid4, hydrolysis oxidation of dichloroacetic acid5 and
oxalic acid electrochemical reduction6,7. But all these methods
have many disadvantages such as huge facilities, large invest-
ments, complex mechanical works and potential environmental
pollutions, high costs for operating and maintaining. Thus,
the methods mentioned above are not satisfying in practical
application, it is urgent to seek a reasonable and economic
method.
NaOH
Cl2CHCOOCH3 + H3COH
→
(H3CO)2CHCOONa + NaCl
(H3CO)2CHCOONa + H2SO4 OCHCOOH + Na SO
→
2
4
EXPERIMENTAL
Methyl dichloroacetate is a by-product when producing
methyl chloroacetate by using methanol esterify mother liquor
of chloroacetic acid (contains 30-35 % dichloroacetic acid).
The synthesis process of the glyoxalic acid using the methyl
dichloroacetate as the raw material has the characteristics of
simple process, low costs and good product quality. At the
same time it also takes advantage of the mother liquor of
chloroacetic acid and reduces emissions to the environment.
As a new heating technology, the microwave extraordi-
narily improves the efficiency and yields and shortens reaction
Ethyl dichloroacetate (Industry grade, purity 99.9 %), w
(sulfuric acid) = 98 %, sodium hydroxide (AR, 96.0 %),
potassium hydroxide (AR, 85.0 %), sodium carbonate (AR,
99.8%), sodium bicarbonate (AR, 99.5 %), sodium acetate
(AR, 99.0 %), potassium carbonate (AR, 99.0 %) and methanol
(AR, 99.5 %). Microwave chemistry reactor (Gongyi City
Yuhua Instrument CO., LTD) with microwave frequency 2450
MHz, power 80-800 W.
Synthesis of glyoxalic acid: In a 100 mL, three-necked,
round-bottomed flask a certain quantity of methanol should

1996 Niu et al.
Asian J. Chem.
be added, then a moderate amount of sodium hydroxide to
join in methanol, fully stirring and dissolving. After 1 h, a
quantity of methyl dichloroacetate was added to methanol
under different conditions and the solid was filtered out after
a period of heat-preservation stirring. The cake was washed
three times with a moderate amount of methanol, merging of
filtrates. An appropriate amount of sulfuric acid (50 %) was
added into the filtered liquor to adjust the pH value to about
2-3 after the separation of salts, stirring 1.5 h keeping the
temperature at 30 °C or below, then filter out solid. The cake
was washed three times with a moderate amount of methanol,
merging of filtrates, obtaining glyoxalic acid solution.
Determination of glyoxalic acid9: About 1 g solution of
glyoxalic acid was added into 25 mL distilled water and
10 mL sulfuric acid (1:5), heated to 60-80 °C. Titration end-
points can be identified by the fact that when using 0.02 mol
L- 1 standard KMnO4 solution titrant to titrate the solution to
red and which do not fade about 30 s. The concentration of
glyoxalic acid can be calculated according to the following
equation:
rature continues to raising, heat effect may have some damage
on the active ingredients of the glyoxalic acid, so 75 °C is a
suitable temperature.
Effect of reaction time on the yield of glyoxalic acid:
In a mixed solvent of 40 mL methanol, 7.5 g sodium hydroxide
and 5.2 mL (0.5 mol) methyl dichloroacetate, the reaction
would be efficiently carried out at 75 °C, at various time in the
same power of microwave radiation for 6 h. And then deter-
minate the yield of glyoxalic acid. Compared those with
conventional heating, the results are shown in Fig. 2.
The yield of glyoxalic acid rises with reaction time
increasing. The reaction time is longer, the faster the reactions
rate will be. But the improvement is low when the reaction
time is above 6 h and the basic yield maintains around 80 %.
This may be that as the extension of reaction time, the local
temperature will be too high and might bring in much by-
products, as well as reaction material methanol evaporation,
glyoxalic acid decomposition and carbonization and thus cause
the production rate to drop, so 6 h is a suitable reaction time.
It only took 4 h for microwave irradiation but 12 h for conven-
tional heating when yield of glyoxalic acid reaches 70 %. It is
clear that the reaction rate under microwave heating is 3 times
higher than that of conventional heating.
N× V× 74
×100
Glyoxalic acid % =
G ×1000
where, N represents molar concentration of standard KMnO4
solution, mol L-1.V represents consumption volume of KMnO4
solution, mL. G represents sample weight, g. The molecular
weight of glyoxalic acid is 74.
85
Microwave
Conventional heating
80
75
70
65
60
55
RESULTS AND DISCUSSION
Effect of reaction temperature on the yield of glyoxalic
acid: The yield of glyoxalic acid was measured at different
temperatures with same power of microwave radiation for 6 h,
in the mixed solvent of 40 mL methanol, 7.5 g sodium
hydroxide and 5.2 mL (0.5 mol) methyl dichloroacetate
(Fig. 1).
Results in Fig. 1 are shown that the yield increases with
the rise of temperature, but the extent of the improvement of
yields will decrease when the temperature is above 65 °C.
Due to microwave treatment, with solution temperature rising
gradually, molecules vibrate faster and friction increases, which
are good for the production of the glyoxalic acid. If the tempe-
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16 17
Time (h)
Fig. 2. Effect of different reaction time on the glyoxalic acid yield
Effect of different alkali on the yield of glyoxalic acid:
The methyl dichloroacetate and different kinds of alkali molar
ratio 3.75:1 were respectively added to 40 mL of methanol, in
the same power of microwave with methyl dichloro-acetate
radiation 6 h, determination of glyoxalic acid (Table-1).
Results showed that the different alkali has a relatively
great different influence on the glyoxalic acid production rates.
85
80
75
70
65
60
55
50
45
TABLE-1
EFFECT OF DIFFERENT ALKALI ON
THE YIELD OF GLYOXALIC ACID
Quality
(g)
Temperature
(°C)
Methanol
(mL)
Yield
(%)
Alkali
CH3COONa
Na2CO3
K2CO3
15.4
19.9
25.9
15.8
10.5
7.50
65
65
65
65
75
75
40
40
60
40
40
40
3.68
5.20
5.70
40
50
60
Temperature (°C)
Fig. 1. Effect of different temperature on the glyoxalic acid yield
70
80
90
NaHCO3
KOH
7.60
77.00
80.40
NaOH

Vol. 26, No. 7 (2014)
Synthesis of Glyoxalic Acid Using Methyl Dichloroacetate by Microwave Method 1997
It is seen that NaOH as a reactant is a suitable alkali with high
yield.
NaOH/C3H4O2Cl2 molar ratio, the yields are improving, but
the improvement are low when the NaOH/C3H4O2Cl2 molar
ratio is above 4.25:1, at the same time consumption of sulfuric
acid increases. The increase of dosage of sodium hydroxide
could increase the yield of production in certain scope, but
the excess increasing of them might bring in much by-products
and would increase the loss of glyoxalic acid in post-proce-
ssing, so 4.00 molar ratio of NaOH/C3H4O2Cl2 is suitable.
Effect of NaOH/C3H4Cl2O2 molar ratio on the yield of
glyoxalic acid: 5.2 mL (0.5 mol) methyl dichloroacetate, in
the same power of microwave radiation 6 h, the reaction would
be efficiently carried out at 75 °C, effects of the NaOH/
C3H4Cl2O2 molar ratio on the yield of glyoxalic acid are shown
in Table-2 and Fig. 3.
Conclusion
TABLE-2
EFFECTS OF NaOH/C3H4O2Cl2 MOLAR RATIO
ON THE YIELD OF GLYOXALIC ACID
Microwave irradiation was used to synthesize glyoxalic
acid from methyl dichloroacetate. Under the same reagent
application, in comparison with the conventional heating, the
microwave irradiation greatly reduced the synthesis time. It
only took 4 h for microwave irradiation but 12 h for conven-
tional heating if the yield of glyoxalic acid reaches 70 %. It is
clearly that the reaction rate under microwave heating was 3
times higher than that of conventional heating.
NaOH/ C3H4Cl2O2
molar ratio
3.25:1
Methanol (mL)
Yield (%)
1
2
3
4
5
6
34.5
36.5
40.0
41.5
45.0
48.0
76.4
78.0
80.4
82.2
84.6
79.9
3.50:1
3.75:1
4.00:1
4.25:1
Under the optimum microwave irradiation condition, the
yield of glyoxalic acid was 84 %, which is higher than the
yield (72 %) obtained under traditional heating method.
The reason may be that both quantity and energy activated
molecules in microwave field is higher than that in thermal
environment and the distribution is more uniform at the same
temperature.
4.50:1
In the synthesis of glyoxalic acid process, the synthesis
of dimethoxy acetate sodium are the key steps in the reaction8.
The results are shown in Table-2 and Fig. 3, the NaOH/
C3H4O2Cl2 molar ratio has a relatively great influence on the
glyoxalic acid production rates. With the increasing of the
In conclusion, the microwave irradiation can greatly
reduce the synthesis time, increase the production yield and
meet the development requirements of green chemistry.
86
84
82
80
78
76
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3.2
3.4
3.6
3.8
4.0
4.2
4.4
4.6
9. X.Q. Liu, J.Y. Liu and Y.F. Zhang, Chem. Bioeng., 6, 42 (2004).
NaOH/C3H4O2Cl2 molar ratio
Fig. 3. Effect of NaOH/C3H4O2Cl2 molar ratio on the yield of glyoxalic
acid